1. Field of the Invention
The present invention relates to cylindrical type alkaline storage batteries.
2. Description of the Related Art
There has been a strong demand for cylindrical type alkaline storage batteries with higher capacity, especially, higher-capacity nickel-hydrogen storage batteries. Specifically, for AA size batteries, development of nickel-hydrogen storage batteries with a volumetric energy density higher than 400 Wh/l is demanded.
A high-capacity AA size nickel-hydrogen storage battery is disclosed, for example, in Unexamined Japanese Patent Publication No. 2005-056682, in which the battery capacity is enhanced by using a positive electrode plate with an increased thickness. In this battery, the positive electrode plate constituting an electrode assembly is rolled up such that the number of turns thereof is greater than or equal to three and at the same time is smaller than four, and immediately after the rolling, the electrode assembly has a nearly round cross-sectional form. Consequently, a larger-sized electrode assembly or positive electrode plate can be received in the container of the battery, thus making it possible to increase the battery capacity.
A cylindrical type alkaline storage battery with higher capacity can certainly be obtained by increasing the thickness of the positive electrode plate, as disclosed in Unexamined Japanese Patent Publication No. 2005-056682. Increasing the thickness of the positive electrode plate, however, entails increase in current density during the charging/discharging and thus is not desirable from the point of view of quick charging characteristic and discharging characteristic. Also, increase in the thickness/density of the positive electrode plate lowers the productivity of the positive electrode plate fabrication process as well as the battery assembling process. Further, it is difficult to maintain the quality of the obtained positive electrode plates and batteries.